This implies that any misfortune or calamity that may afflict people, besides having a certain cause, it is also a means of testing, in order to mark out those who are truthful from those who lie exposing them to the sight of their brothers. In other word, to make the line of each group distinct from that of the others:
``That which afflicted you the day in which the two hosts encountered in OHUD, was by the permission of Allah.''
Here Allah's permission is His Will which is usually manifested in the LAW of Cause and Effect.
The verse ends in: ``that Allah may make known the faithful from among the unfaithful, exposing them to the sights.''